The present disclosure relates to a display device, a pixel circuit used in the display device, an electronic apparatus including the display device, and a method of driving the display device.
At present, a display device including a pixel circuit (referred to as “a pixel” as well) having a display element (referred to as “an electrooptic element” as well), and an electronic apparatus including the display device are generally utilized. There is known a display device which uses an electrooptic element in which a luminance is changed depending on a voltage applied thereto or a current caused to flow therethrough as a display element in a pixel. For example, the electrooptic element in which the luminance is changed depending on the voltage applied thereto is typified by a liquid crystal display element. On the other hand, the electrooptic element in which the luminance is changed depending on the current caused to flow therethrough is typified by an Organic Electro Luminescence element (Organic EL element or Organic Light Emitting Diode (OLED)) (hereinafter referred to as “an organic EL element”). An organic EL display device using the latter organic EL element is a so-called self-emission type display device using the electrooptic element, as a self-emission element, as the display element in the pixel.
Now, in the display device using the display element, both of a passive matrix system and an active matrix system can be adopted as a system for driving the display device. However, the display device utilizing the passive matrix system involves a problem that it may be difficult to realize the large and fine-definition display device although a structure is simple.
For this reason, in recent years, the active matrix system for controlling a pixel signal supplied to a display element which is provided inside a pixel by using a transistor such as an active element which is also provided inside the pixel, for example, an insulated gate field-effect transistor (in general, a Thin Film Transistor (TFT)) as a switching transistor has been actively developed.
In the existing display devices each utilizing the active matrix system, threshold voltages and mobilities of transistors for driving respective display elements are dispersed due to a process change. In addition, the characteristics of the display element are changed with time. Such a dispersion of the characteristics of the drive transistors, and such a change in the characteristics of the elements, such as the display elements, composing the pixel circuit exert an influence on the emission luminance. That is to sway, if image signals having the same level are supplied to all of the pixels, respectively, all of the pixels emit lights with the same luminance and thus the uniformity of the picture ought to be obtained. However, the dispersion of the characteristics of the drive transistors, and the change in the characteristics of the display elements impair the uniformity of the picture. In order to cope with such a situation, the technique for correcting the display nonuniformity due to the dispersion of the characteristics of the elements, such as the transistors and the display elements, composing the pixel circuit within each of the pixel circuits in order to uniformly control the emission luminance over the entire picture of the display device, for example, is proposed in Japanese Patent No. 4240059 or Japanese Patent No. 4240068.
Here, the characteristics of the elements composing the pixel circuit are influenced by the environmental characteristics. However, the technique disposed in Japanese Patent No. 4240059 or Japanese Patent No. 4240068 does not disclose a method of coping with the influence of the environmental characteristics.
The present disclosure has been made in order to solve the problems described above, and it is therefore desirable to provide a display device in which a display nonuniformity phenomenon due to a dispersion of characteristics of elements composing a pixel circuit can be suppressed independently of an environmental change, a pixel circuit used in the display device, an electronic apparatus including the display device, and a method of driving the display device.
In order to attain the desire described above, according to an embodiment of the present disclosure, there is provided a display device including: a display portion; a hold capacitor; a write transistor writing a drive voltage corresponding to a video signal to the hold capacitor; a drive transistor driving the display portion in accordance with the drive voltage written to the hold capacitor; and a pulse width adjusting portion adjusting a width of a pulse signal causing a drive pulse used to drive at least one of the write transistor and the drive transistor so as to correspond to an environmental change.
According to another embodiment of the present disclosure, there is provided a pixel circuit including: a display portion; a hold capacitor; a write transistor writing a drive voltage corresponding to a video signal to the hold capacitor; and a drive transistor driving the display portion in accordance with the drive voltage written to the hold capacitor. A pulse width of a drive pulse used in at least one of the write transistor and the drive transistor is adjustably formed so as to correspond to an environment dependency.
According to still another embodiment of the present disclosure, there is provided an electronic apparatus including: a pixel portion in which display elements each including a display portion, a hold capacitor, a write transistor writing a drive voltage corresponding to a video signal to the hold capacitor, and a drive transistor driving the display portion in accordance with the drive voltage written to the hold capacitor are disposed; a signal generating portion generating a video signal which is to be supplied to the pixel portion; drive lines disposed in the pixel portion and supplying drive pulses in order to drive at least ones of the write transistors and the drive transistors disposed in a predetermined direction; a selecting portion selecting the drive lines; a pulse width adjusting portion adjusting a width of a pulse signal causing the drive pulse used to drive at least one of the write transistor and the drive transistor so as to correspond to an environmental change; and a pulse generating portion generating the pulse signal causing the drive pulse in accordance with a pulse signal outputting the pulse width adjusting portion. The selecting portion supplies the drive pulses to the drive lines, respectively, in accordance with the pulse signal generated in the pulse generating portion.
According to yet another embodiment of the present disclosure, there is provided a method of driving a display device including a pixel portion in which display elements each having a display portion, a hold capacitor, a write transistor writing a drive voltage corresponding to a video signal to the hold capacitor, and a drive transistor driving the display portion in accordance with the drive voltage written to the hold capacitor are disposed. A width of a pulse signal causing a drive pulse used to drive at least one of the write transistor and the drive transistor is adjusted so as to correspond to an environmental change.
In short, in the technique disclosed in this specification, the width of the pulse signal causing the drive pulse used to drive at least one of the write transistor and the drive transistor is adjusted so as to correspond to the environmental change. The drive pulse can be generated in accordance with the pulse signal whose pulse width is automatically adjusted so as to correspond to the environmental change in such a way that the environment dependency of the characteristics of the elements composing the pixel circuit is canceled. Even when the characteristics of the elements composing the pixel circuit are influenced by the environmental characteristics, so that the optimal correction period of time is changed so as to correspond to the environmental change, the drive pulse can be generated in accordance with the pulse signal whose pulse width regulating the processing period of time is automatically adjusted so as to correspond to the environmental change. As a result, the display nonuniformity phenomenon due to the dispersion of the characteristics of the elements composing the pixel circuit can be suppressed independently of the environmental change.
As set forth hereinabove, according to the present disclosure, the display nonuniformity phenomenon due to the dispersion of the characteristics of the elements composing the pixel circuit can be suppressed independently of the environmental change.